The Flop (Floating Point Operations per Second) Rate of MATLAB Code
30 visualizzazioni (ultimi 30 giorni)
Mostra commenti meno recenti
Hello, I know Intel MKL / IPP libraries performance in simple operations (Multiplication, Summation, Matrix Multiplication, Vector Multiplication) gets something like 80-95% of the theoretical performance of the CPU (Measured in FLOPS).
http://software.intel.com/en-us/articles/parallelism-in-the-intel-math-kernel-library http://software.intel.com/en-us/intel-mkl
Yet, doing so using MATLAB I get much worse results.
I have this simple script:
numElements = 2 ^ 16;
numIter = 100;
vecX = randn(numElements, 1, 'single');
vecY = randn(numElements, 1, 'single');
initTime = tic();
for ii = 1:numIter
vecX .* vecY;
end
stopTime = toc(initTime);
gFlops = (numElements * numIter) / stopTime
Yet I get only 1.1 GFLOPS on my i7-860 Which should be closer to 2.8GHz (Frequency) * 4 (Cores) * 4 (Single Precisio Operations per Cycle as SSE Vector - 128 Bit) = 44.8 GFLOPS.
Yet I get something like 1.4 GFLOPS. Which is only 3% of the theoretical performance.
How can MATLAB be so inefficient?
2 Commenti
Amit
il 28 Gen 2014
BTW, MATLAB is only using 1 core, I'd believe. And for a benchmark, is there anything else running besides MATLAB?
Risposta accettata
Amit
il 28 Gen 2014
Modificato: Amit
il 28 Gen 2014
I don't think the way you're trying to calculate flops here is right. Even if one assumes that you can calculate Flops like this, you're missing out many overheads that matlab is doing. For example, try something like this:
numElements = 2 ^ 18;
numIter = 100;
vecX = randn(numElements, 1, 'single');
vecY = randn(numElements, 1, 'single');
initTime = tic();
% for ii = 1:numIter
% vecX .* vecY;
% end
vecX + vecY; % I used +, but you can switch to .* as well
stopTime = toc(initTime);
gFlops = (numElements * numIter) / stopTime
And see if you see any difference. I am pretty sure you will. Remember, for loop is slow.
4 Commenti
Walter Roberson
il 16 Giu 2019
tic and toc only provide elapsed time information, which is not the same as the amount of computation done, as elapsed time can include time that the operating system suspended MATLAB in order to work on something else.
Più risposte (1)
Walter Roberson
il 28 Gen 2014
single() is often slower than double()
Your arrays are not that big; I am not sure that it is kicking in calls to the libraries.
2 Commenti
Walter Roberson
il 29 Gen 2014
Try with timeit. Or if you have an older MATLAB that does not have that built-in, you can get timeit from the File Exchange.
Vedere anche
Categorie
Scopri di più su Filter Analysis in Help Center e File Exchange
Prodotti
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!